Adhered roof structure with two component adhesives

ABSTRACT

A roof structure comprises a roof membrane and a roof substrate. A first surface of the roof membrane is adhered to the roof substrate by a two component adhesive, the adhesive being capable of adhering the first surface of the roof membrane to the roof substrate without the use of a high VOC solvent. The two component adhesive includes a Michael donor and a Michael acceptor, and the Michael donor and the Michael acceptor react to form an adhesive film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of Non-Provisionalapplication Ser. No. 15/581,926, filed Apr. 28, 2017, which claims thebenefit and priority to Provisional Application Ser. No. 62/329,672,filed Apr. 29, 2016, the disclosures of which are expressly incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to adhered roof structures.

BACKGROUND

Membrane roofs utilize a membrane formed from polymers such as ethylenepropylene diene monomer rubber (EPDM), thermoplastic olefin (TPO), orpolyvinyl chloride (PVC) as a waterproof barrier. The membrane must besecured on the roof in some way. There are a variety of differentmethods to do this including ballast (i.e., gravel), mechanicalfasteners, and adhesives.

The performance and regulatory demands on adhesive and other materialscontinues to evolve. Typical adhesives used in roofing applicationsinclude polychloroprene- or neoprene-based adhesives. However, theseconventional roofing adhesives have aromatic solvents such as toluene orxylenes. These solvents are under increasing environmental pressures asVOC regulations tighten.

SUMMARY

In an embodiment, the present invention provides a roof structureincluding a roof membrane and a roof substrate. A first surface of theroof membrane is adhered to the roof substrate by a two componentadhesive, the adhesive being capable of adhering the first surface ofthe roof membrane to the roof substrate without the use of a high VOCsolvent. The two component adhesive includes a Michael donor and aMichael acceptor; the Michael donor and the Michael acceptor react toform an adhesive film.

The objects and advantages of present will be further appreciated inlight of the following detailed descriptions and drawings in which:

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a cross sectional view partially broken away of a roofstructure utilizing an embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention are directed to adhered roofstructures and two component adhesives, which may be used in adheredroof structures. With reference to the FIGURE, an exemplary roofstructure 10 includes a supporting surface 12 (e.g., roof substrate orroof deck) covered with an insulating foam panel 14. The roofingmembrane 16 in the illustrated embodiment has an outer polymeric surface18 and an inner fleece or fibrous layer 22. An adhesive 24 is utilizedto adhere the membrane 16 to the foam panel 14, which is mechanicallyattached to the supporting surface 12.

A wide variety of different membranes can be used in embodiments of thepresent invention, either with or without a fleece layer. These can bethermoplastic membranes such as polyvinyl chloride and thermoplasticolefin, as well as thermosets such as EPDM, as well as other single plyroofing membranes. In an embodiment, the membrane 16 is an EPDMmembrane, which includes the fleece layer 22. The manufacture of such anexemplary product is disclosed in U.S. Pat. No. 5,620,554, thedisclosure of which is hereby incorporated by reference in its entirety.

The membrane is adhered to insulating foam panels 14 by adhesive layer24. If foam panels are not present, the membrane 16 could be adhered toroof substrate 12 by the adhesive layer 24.

More specifically, the two component adhesive used in embodiments of thepresent invention that forms the adhesive layer 24 includes an ambientcuring adhesive system based on a Michael reaction in which a Michaeldonor and a Michael acceptor react to form a stable polymeric filmcapable of bonding to roofing materials (e.g., membrane 16) andsubstrates (e.g., foam panel 14) with high adhesion. In an embodiment,the adhesive includes bis-acetoacetate as the Michael donor anddiacrylate as the Michael acceptor and may be cured at ambient roomtemperature. Additional suitable Michael acceptors include vinylketones, nitro ethylenes, α,β-unsaturated aldehydes, vinyl phosphonates,acrylonitrile, vinyl pyridines, azo compounds and even p-keto acetylenesand acetylene esters. Additional suitable Michael donors includenon-enolate nucleophiles such as amines, thiols, and phosphines; thesereactions are typically referred to as Michael type additions.

The Michael reaction between diacrylate and bis-acetoacetate is shownbelow. The diacrylate may be a higher functional acrylate, such as atriacrylate. Suitable multi-functional acrylates are made by SigmaAldrich and Cray Valley. st. Further, it will be recognized that R andR′ can vary widely in their composition, which impacts reactivity,adhesion, and film physical properties (e.g., hardness, elongation, tearresistance, and heat resistance). Exemplary compounds for R and R′include, without limitation, shorter chain alkyls (e.g., C4-C10) andlonger chain alkyls that (e.g., C140-C210, or average 2000-3000 MW).

The Michael reaction includes a catalyst and does not require anexternal factor (e.g., moisture, air, UV, etc.) to drive the reaction.In addition, this reaction chemistry does not produce any by-productsduring the reaction. The catalyst activates the Michael donors andenables the addition reaction across a carbon-carbon multiple bond ofMichael acceptors.

Typical catalysts include organic bases, such as tetramethylguanidine(TMG), triethylamine, 1,8 diazabicyclo[5.4.0]undec-7-ene (DBU), and 1,5diazabicyclo[4.3.0]non-5-ene (DBN), as well as inorganic bases such aspotassium carbonate, boron trifluoride, aluminum trifluoride, aluminumtrichloride, and zinc chloride.

In embodiments of the invention, the adhesive formulation may includeadditives depending on the particular application. For example, theadhesive may include a variety of materials that increase the usefulnessof the adhesive in roofing applications. Exemplary additives include,without limitation, tackifiers, diluents, viscosity modifiers,stabilizers, fillers, adhesion promoters, and/or other materials.

Tackifiers used in this type of adhesive include, but are not limitedto, resins (e.g., aliphatic and aromatic hydrocarbon, phenolic, ketonic,rosin, terpene, etc.) and liquid polymers (e.g., polyisobutylene, EPDM,etc.). Diluents and viscosity modifiers may be used to regulate therheology of the adhesive. Exemplary diluents and viscosity modifiersinclude, but are not limited to, oils (e.g., paraffinic, aromatic,naphthenic, soy, etc.), plasticizers (e.g., phthalates, dibasic ester,adipate esters, epoxidized esters, etc.), or viscosity modifying liquidsor solids (e.g., polymers, thixotropes, clays, etc.). While the additionof such components to conventional adhesives (e.g., based on solvent,water, or polyurethane) alters the reactivity of the components of theadhesive, the Michael reaction may not be affected, which improves theversatility of the particular adhesive composition.

Formulas for the Michael adhesive may include a 1:1.2 molar ratio ofbis-acetoacetate to diacrylate, for example. Formulas for the adhesivemay use the combination of bis-acetoacetate and diacrylate at the 1:1.2molar ratio as a basis to represent 100 parts per hundred resin (phr).Embodiments may include an adhesive formula having: 100 phr ofbis-acetoacetate and diacrylate; 0.5 to 5 phr of a catalyst; 0 to 250phr of a resin; 0 to 250 phr of a liquid polymer; and 0 to 20 phr of aviscosity modifier. For example, in an embodiment, the adhesivecomprises: 100 phr of bis-acetoacetate and diacrylate; 1 phr of a DBUcatalyst; and 11 phr of an aliphatic hydrocarbon resin. In anotherembodiment, the adhesive comprises: 100 phr of bis-acetoacetate anddiacrylate; 1 phr of a DBU catalyst; and 11 phr of polyisobutylene.

In embodiments of the invention, the ambient curing two componentadhesive is applied to a roofing substrate to adhere a roofing membraneto the roof structure. For example, with reference to the FIGURE, theadhesive 24 is applied to the foam panel 14 (which is typicallymechanically-fastened to the roof substrate 12), and the roofingmembrane 16 is placed over the adhesive-coated panels. The adhesive maybe applied using a low VOC nonaromatic or regulated solvent or byapplying the components (e.g., oligomers or monomers) without solvent.The membrane 16 can be applied to the adhesive layer 24 immediatelyafter the application of adhesive layer 24.

Typically, the components of the adhesive are mixed with the catalyst atthe construction site and sprayed or otherwise applied on the membranesurface and/or on the surface of the roof substrate. Alternatively, oradditionally, an encapsulation process may be used to separate one ofthe components of the adhesive system (e.g., the catalyst, Michaeldonor, or Michael acceptor) from the other components in the reaction.The adhesive including the encapsulated catalyst would be applied to thesubstrate, and the catalyst released to initiate the curing process viaa mechanical shear event. For example, a roller may be used to releasethe catalyst after the adhesive has been applied. It should berecognized that the adhesive composition, including any additives andcatalyst, may be varied based on the desired curing time, the adhesiveand strength properties required in the intended application, and thecompatibility of the composition with the selected membrane andinsulation substrate.

The Michael adhesives disclosed herein can also be used to bondoverlapped sections of adjacent membrane sheets to form lap seams.

The adhesive properties of interest in roofing membranes ofpoly(hydrogenated butadiene) based Michael donors and acceptors wereevaluated. The poly(hydrogenated butadiene) based Michael donors andacceptors demonstrated universal adhesive performance with EPDM, PVC,and TPO roofing substrates. Poly(hydrogenated butadiene) based Michaeldonors and acceptors were synthesized using a facile approach involvingmodification of commercially available Krasol® diols. These reactiveoligmeric diols offer hydrogenation levels greater than 97%, M_(n)values of 2,000 and 3,000 g/mol, excellent thermal stability, goodweatherability, hydrophobicity, low color, high clarity, and low glasstransition temperatures (T_(g)=−55° C.), affording their compatibilityfor applications involving acid and base resistance, adhesion, asphaltmiscibility, electrical insulation, and low temperature flexibility. Thesynthesis of Krasol® diacrylates and reaction conditions involving 2,000g/mol Krasol® diol are shown below as an example synthetic procedure.

A two-neck 500 mL round-bottomed flask, equipped with a 50 mL additionfunnel containing acryloyl chloride (5.2 g, 0.055 mol) in anhydrous DCM(20 mL), was charged with 2,000 g/mol Krasol® diol (50 g, 0.025 mol) andanhydrous K₂CO₃ (10.37 g, 0.075 mol) and was sealed with a rubberseptum. Anhydrous DCM (110 mL) was cannulated into the reaction flask,and an ice bath was assembled to cool the reaction contents to 0° C.Acryloyl chloride was added dropwise overnight and the reaction wasallowed to warm to 23° C. Salt byproduct was filtered and the organicsolute was washed 3× with H₂O. DCM was removed under reduced pressure (5mmHg) and the product was isolated as a clear liquid and was dried invacuo at 23° C. (48.23 g, 96% yield). ¹HNMR (400 MHz, CDCl3): 6.47 (d,2H), 6.22 (dd, 2H), 5.77 (d, 2H), 4.13 (m, 4H), 0.75-1.5 (polymerbackbone). Molecular weight determination from ¹HNMR showed M_(n)=2,200.

An example synthetic route for achieving these bisacetoacetate donorsfollows. 2,000 g/mol Krasol® diol (10.0 g, 10 mmol) and tBuAcAc (6.3 g,40 mmol, 4 equiv.) were charged to a two-necked 100-ml flask, equippedwith a short-path distillation head, receiving flask, and magneticstint. The mixture was maintained at 150° C. for 3 h and vacuum (0.1mmHg) was applied to remove the tert-butanol byproduct and excesstBuAcAc. An additional 6.3 g tBuAcAc was added and heating continued for3 h at 150° C. in order to ensure quantitative functionalization. Vacuum(0.1 mmHg) at 150° C. was applied to remove volatile starting reagentsand reaction by-products. ¹HNMR spectroscopy of the Krasol® BisAcAcoligomers confirmed the desired composition. ¹HNMR (400 MHz, CDCl3) ofthe 2000 g/mol Krasol® BisAcAc: 0.75-1.5 (polymer backbone), 1.24 ppm(dd, 6H, CHCH₃OAcAc), 2.26 ppm (s, 6H, COCH₂COCH₃), 5.08 ppm (m, 4H,CH₂CHCH₃OAcAc), 5.29 ppm (s, enol C═CH—C═O).

Mixing equal molar ratios of these acceptors and donors with catalyticDBU enables a 2-component reactive curing system and provides acrosslinked Michael network under ambient conditions (23° C.). Catalystconcentration, temperature, and crosslinking agent compositions tune thereaction kinetics, facilitating cure times that range from 10 min to 300min.

Rheological analysis elucidated crosslinking reaction kinetics,revealing the effects of catalyst concentration, temperature, andacceptor/donor M_(n) on gelation time. A steady-strain oscillationexperiment monitored the storage and loss moduli (G′, G″) as theviscous, 2-component curing system crosslinked into an elastic,free-standing film network. The G′ and G″ crossover point representedthe viscoelastic transition point, known as the gel point, and occurredat various times as a function of the tested variables. In the case ofcatalyst concentration, increasing DBU concentration from 1 wt. %, 2 wt.%, and 3 wt. % afforded faster gelation in tunable time frames of 80min, 60 min, and 15 min (for M_(n) 2,000 g/mol or 3,000 g/mol). At 2 wt.% DBU catalyst, the gelation point was approximately 60 min.

Temperature variation is a major concern for roofing adhesion. To becompetitive, an adhesive should exhibit high performance adhesionyear-round during all seasons. Rheological studies demonstratedcrosslinking efficiency for the Michael adhesives disclosed herein underextreme cold (−10° C.), ambient (25° C.), and extreme heat (50° C.)conditions (for M_(n) 2,000 g/mol or 3,000 g/mol). Steady-strainoscillation studies at these temperatures, with a constant catalystconcentration of 1 wt. % DBU, demonstrated Michael network formation forall temperatures. Crosslinking behavior occurred the slowest at −10° C.,presumably corresponding to increased oligomeric chain rigidity anddecreased intermolecular motion. Increasing the temperature to ambientconditions increased chain mobility and enabled crosslinking to occurwithin 80 min. The fastest crosslinking time (20 min) occurred at 50°C., where intermolecular motion approached fluidic behavior and theaddition reaction was kinetically favored. M_(n) also influenced gettime, revealing slightly longer time frames for curing systems involving3,000 g/mol vs. 2,000 g/mol Krasol® oligomers under comparabletemperatures. Most evident, −10° C. corresponded to the strongest effectof M_(n) on gel time and indicated a 40% increase in gel time for the3,000 g/mol curing system in comparison to the 2,000 g/mol system.

A 2000 g/mol Krasol® bisacetoacetate was reacted with the commerciallyavailable 1,4-butanediol diacrylate (1,4-BDA). Rheologicalinvestigations elucidated gel time variation (min) as a function oftemperature (° C.) (for M_(n) 2,000 g/mol or 3,000 g/mol). Comparable toprevious temperature studies, the slowest gel time occurred at −10° C.and gel time increased with increasing temperature. Crosslinkingoccurred rapidly at both 25 and 50° C., faster in comparison to curingsystems involving Krasol® diacrylates. For the curing system involving1,4-RDA, gel time occurred within 10 min as opposed to 30 min forsystems involving Krasol® diacrylates. This presumably resulted from themolecular weight differences in 1,4-BDA and Krasol® diacrylates.

Tuning gel times of crosslinked Michael networks provides flexibilityduring rooftop applications, allowing construction employees to activateMichael adhesives according to roof dimensions and membrane supply.These solvent-free adhesives offer low viscosity for coating and requireno solvent evaporation prior to adhesion. Gelation occurs within minutesand 24 h ensures complete formation of crosslinked networks. 180° peeltests investigated adhesion strength and failure modes of cured membranesamples including EPDM to EPDM, PVC to PVC, and TPO to TPO substrates.These studies provided insight into adhesive compatibility with thevarious roofing membranes, and provided peel strength data in comparisonto conventional commercial bonding adhesives. Michael adhesivesinvolving 2000 g/mol Krasol® bisacetoacetate behaved as a universalcuring system for three different roofing membranes, revealingcomparable peel strength to the highest performing, solvent-basedcommercial adhesives and improved strength in comparison to low VOCadhesives. Table I reports average peel loads and failure modes for allroofing samples with Michael adhesives along with suitable adhesivecontrols. Advantageously, all Michael adhesive samples revealed cohesivefailure and suggested adhesive dependence on strength of the crosslinkednetworks.

TABLE 1 Failure Average Average Substrate/adhesives Mode Load (N) Load(lbs) EPDM/2K Krasol ® Cohesive 4.0 0.9 EPDM/2K Krasol ®: 1,4 BDACohesive 4.0 0.9 EPDM/Neoprene Cohesive 3.5 0.8 EPDM/Low VOC Adhesive1.5 0.3 PVC/2K Krasol ® Cohesive 4.0 0.9 PVC/2K Krasol ®: 1,4 BDACohesive 3.5 0.8 PVC/Low VOC Cohesive 3.5 0.8 TPO/2K Krasol ® Cohesive10.0 2.3 TPO/2K Krasol ®: 1,4 BDA Cohesive 5.0 1.1 TPO/TPO Cohesive 4.51.0 TPO/Low Cohesive 5.0 1.1

The Michael adhesives described herein represent a green alternative tosolvent-based roofing adhesives and provide a large host of donors andacceptors, with optional catalysts. The Michael adhesives are tunablefor roofing membrane substrates. The rheological studies elucidatedeffects of catalyst concentration, temperature, M_(n), donor/acceptorcompositions on gelation times, revealing tunable gel times in a 10-300min time range for example. 180° peel tests revealed crosslinked Michaelnetworks as high performing adhesives for binding roofing substrates,exhibiting comparable peel strengths to traditional solvent-basedadhesives and improved strengths to Low VOC adhesives.

While specific embodiments have been described in considerable detail toillustrate the present invention, the description is not intended torestrict or in any way limit the scope of the appended claims to suchdetail. The various features discussed herein may be used alone or inany combination. Additional advantages and modifications will readilyappear to those skilled in the art. The invention in its broader aspectsis therefore not limited to the specific details, representativeapparatus and methods and illustrative examples shown and described.Accordingly, departures may be made from such details without departingfrom the scope of the general inventive concept.

What is claimed is:
 1. A roof structure comprising: a roof membrane; asupporting surface; and a foam panel, wherein a first surface of theroof membrane is adhered to a first surface of the foam panel by a twocomponent adhesive, the adhesive being capable of adhering the firstsurface of the roof membrane to the first surface of the foam panelwithout the use of a high VOC solvent, and wherein the two componentadhesive includes a Michael donor and a Michael acceptor, and whereinthe Michael donor and the Michael acceptor react to form an adhesivefilm; and wherein a second surface of the foam panel is attached to thesupporting surface, and wherein the adhesive comprises: 100 phr of theMichael donor and the Michael acceptor; 0.5 to 5 phr of a catalyst; 0 to250 phr of a resin; 0 to 350 phr of a liquid polymer; and 0 to 20 phr ofa viscosity modifier.
 2. The roof structure claimed in claim 1, whereinthe Michael donor is selected from the group consisting of:bis-acetoacetate, a vinyl ketone, a nitro ethylene, an α,β-unsaturatedaldehyde, a vinyl phosphonate, acrylonitrile, vinyl pyridine, an azocompound, a p-keto acetylene, an acetylene ester, and a non-enolatenucleophile.
 3. The roof structure claimed in claim 1, wherein theMichael acceptor is a multi-functional acrylate.
 4. The roof structureclaimed in claim 1, wherein the Michael donor is bis-acetoacetate andthe Michael acceptor is diacrylate.
 5. The roof structure claimed inclaim 4, wherein a molar ratio of bis-acetoacetate to diacrylate is1:1.2.
 6. The roof structure claimed in claim 1, wherein the Michaeldonor and the Michael acceptor are poly (hydrogenated butadiene) based.7. The roof structure claimed in claim 1, wherein the catalyst isencapsulated.
 8. The roof structure claimed in claim 1, wherein theadhesive includes one or more additives selected from the groupconsisting of tackifiers, diluents, viscosity modifiers, andstabilizers.
 9. The roof structure claimed in claim 1, wherein the roofmembrane is selected from the group consisting of polyvinyl chloride(PVC), thermoplastic olefin (TPO), and ethylene propylene diene monomerrubber (EPDM).
 10. The roof structure claimed in claim 1, wherein thefoam panel is mechanically fastened to the supporting surface.
 11. Theroof structure claimed in claim 7, wherein the catalyst is released viaa mechanical shear event.
 12. The roof structure claimed in claim 1,wherein the adhesive comprises: 100 phr of the Michael donor and theMichael acceptor; 1 phr of a DBU catalyst; and 11 phr of an aliphatichydrocarbon resin.
 13. The roof structure claimed in claim 1, whereinthe adhesive comprises: 100 phr of the Michael donor and the Michaelacceptor; 1 phr of a DBU catalyst; and 11 phr of polyisobutylene. 14.The roof structure claimed in claim 1, wherein the adhesive filmdemonstrates crosslinking efficiency at least between −10° C. and 50° C.15. The roof structure claimed in claim 1, wherein a composition of theMichael donor and the Michael acceptor has a tunable gel time in a rangeof 10 minutes to 300 minutes.